Leak-compensated proportional assist ventilation

• US 8,267,085 B2
• Filed: 03/20/2009
• Issued: 09/18/2012
• Est. Priority Date: 03/20/2009
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Jafari, Mehdi M., Jimenez, Rhomere S., Upham, Gail F., Aviano, Jeffrey K.
• Primary Examiner(s): Thanh, Loan
• Assistant Examiner(s): Philips, Bradley
• Application Number:
  US12/408,408
• Publication Number:
  US 20100236553A1
• Time in Patent Office: 1,278 Days
• Field of Search: 128/202.22, 128/204.18, 12820421-20423, 128/200.24
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0057 Pumps therefor
• CPC Class Codes: A61M 16/0063 Compressors
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/04 Tracheal tubes catheters in general A61M25/00
• CPC Class Codes: A61M 16/0666 Nasal cannulas or tubing devices for improving normal breathing through the nose A61F5/08; nose filters A62B23/06; outside holding devices A61M25/02
• CPC Class Codes: A61M 16/0816 Joints or connectors
• CPC Class Codes: A61M 16/0875 Connecting tubes
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0033 electrical
• CPC Class Codes: A61M 2205/15 Detection of leaks
• CPC Class Codes: A61M 2205/505 Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

This disclosure describes systems and methods for compensating for leakage when during delivery of gas from a medical ventilator in a proportional assist mode to a patient. The technology described herein includes systems and methods to compensate the delivery of PA ventilation for leakage in the patient circuit by using leak-compensated lung flows as well as leak-compensated respiratory mechanics parameters (lung compliance and lung resistance) estimated in a manner that compensates for elastic and inelastic leaks from the ventilation system.

Claims

1. A method of compensating for leakage in a ventilation system the method performed by the medical ventilator having a processor communicatively coupled to memory, the memory storing instructions that when executed by the processor cause the ventilator to perform the method during delivery of proportional assist ventilation to a patient, the method comprising:

monitoring an instantaneous flow in the ventilation system based on one or more measurements of pressure and flow in the ventilation system;

modeling by the processor leakage from the ventilation system as a first leakage component through a first orifice of a fixed size and a second leakage component through a second orifice of a varying size, wherein the first and second leakage components are different functions of instantaneous pressure in the ventilation system;

estimating a leak-compensated instantaneous lung flow of gas inhaled or exhaled by the patient based on the one or more measurements, the first leakage component and second leakage component;

using the leak-compensated lung flow and a predetermined respiratory mechanics model to estimate a leak-compensated lung compliance and a leak-compensated lung resistance; and

calculating a pressure to be delivered to the patient based on the leak-compensated lung flow, the leak-compensated lung compliance and the leak-compensated lung resistance.

2. The method of claim 1 wherein the method uses a dynamic respiratory mechanics model and the method further comprises:

detecting a condition indicating that leak-compensated lung compliance should be calculated;

retrieving one or more previously estimated leak-compensated instantaneous lung flows; and

estimating a leak-compensated lung compliance and a leak-compensated lung resistance using the dynamic respiratory mechanics model and the retrieved one or more previously estimated leak-compensated instantaneous lung flows.

3. The method of claim 2 wherein the dynamic respiratory mechanics model requires input of a lung volume change over a predetermined time period and the method further comprises:

calculating a leak-compensated lung volume change for the predetermined time period based on leak-compensated lung flows associated with the predetermined time period.

4. The method of claim 1 wherein the method calculates at least the leak-compensated lung compliance and the method further comprises:

calculating a leak-compensated lung volume based on the leak-compensated lung flow during an inspiratory phase;

stabilizing the delivery of gas so that the medical ventilator delivers a stable flow of gas at a stable pressure, wherein the stable flow and stable pressure are determined based on the first leakage component and second leakage component at the stable pressure;

maintaining the stable flow of gas at the stable pressure for at least a predetermined time interval; and

calculating the leak-compensated lung compliance based on the leak-compensated lung volume and the stable pressure.

5. The method of claim 4 wherein stabilizing further comprises:

stabilizing the delivery of gas by adjusting the instantaneous flow of gas to be within a predetermined amount of the first leakage component and second leakage component at the instantaneous pressure.

6. The method of claim 4 wherein stabilizing further comprises:

stabilizing the delivery of gas so that the lung flow is practically zero.

7. The method of claim 4 further comprising:

calculating a leak-compensated lung resistance based on the leak-compensated lung compliance and one or more of a previously calculated leak-compensated lung flow, a previously calculated leak-compensated lung volume and a previously measured pressure.

8. The method of claim 4 wherein the stabilizing and maintaining operations are performed at the end of the inspiratory phase.

9. The method of claim 1 wherein the method calculates at least the lung compliance and the method further comprises:

calculating a leak-compensated lung volume based on the leak-compensated lung flow during an inspiratory phase and expiratory phase;

stabilizing the delivery of gas so that the medical ventilator delivers a stable flow of gas at a stable pressure, wherein the stable flow and stable pressure are determined based on the first leakage component and second leakage component at the stable pressure;

maintaining the stable flow of gas at the stable pressure for at least a predetermined time interval; and

calculating the leak-compensated lung compliance based on the leak-compensated lung volume and the stable pressure.

10. The method of claim 1 wherein the method first calculates a leak-compensated lung compliance and then, based on the leak-compensated lung compliance, calculates a leak-compensated lung resistance.

11. A method of compensating for leakage in a ventilation tubing system during delivery of gas from a medical ventilator to a patient the method performed by the medical ventilator having a processor communicatively coupled to memory, the memory storing instructions that when executed by the processor cause the ventilator to perform the method comprising:

receiving a support setting identifying by the processor an amount of proportional assistance to provide to the patient;

identifying an inelastic leakage in the ventilation tubing system as a first function of at least one of a pressure measurement and a flow measurement in the ventilation tubing system;

identifying an elastic leakage in the ventilation tubing system as a second function of at least one of the pressure measurement and the flow measurement in the ventilation tubing system;

estimating circuit compliance and circuit resistance of the ventilation tubing system;

estimating a lung compliance of the patient and a lung resistance of the patient based on the inelastic leakage, the elastic leakage, the circuit compliance, circuit resistance and the at least one of the pressure measurement and the flow measurement in the ventilation tubing system;

delivering ventilation to the patient based on patient effort and the support setting, wherein the patient effort is determined from the inelastic leakage, the elastic leakage, the lung compliance, the lung resistance and the at least one of the pressure measurement and the flow measurement in the ventilation tubing system.

12. The method of claim 11 wherein estimating lung compliance further comprises:

generating a plurality of leak-compensated lung flows associated with a period of time based on the elastic leakage and at least one of pressure measurements and the flow measurements associated with the period of time;

generating a leak-compensated net lung volume for the period of time based on the plurality of leak-compensated lung flows; and

calculating lung compliance using the leak-compensated net lung volume.

13. The method of claim 11 wherein estimating lung compliance and lung resistance further comprises:

generating a plurality of leak-compensated lung flows associated with a period of time based on the elastic leakage and at least one of pressure measurements and the flow measurements associated with the period of time;

generating a leak-compensated net lung volume for the period of time based on the plurality of leak-compensated lung flows; and

calculating lung compliance and lung resistance using the leak-compensated net lung volume, the plurality of leak-compensated lung flows for the period of time and the pressure measurements associated with the period of time.